This invention generally relates to centrifugal pumps, and, more particularly to suction and discharge pump liners for centrifugal pumps used to pump a mixture of solids and carrier liquid.
Centrifugal pumps, as the name implies, employ centrifugal force to lift liquids from a lower to a higher level or to produce a pressure. This type of pump, in its simplest form, comprises an impeller consisting of a connecting hub with a number of vanes and shrouds, rotating in a volute collector or casing (See FIGS. 1 and 2). Liquid drawn into the center, or eye, of the impeller is picked up by the vanes and accelerated to a high velocity by rotation of the impeller. It is then discharged by centrifugal force into the casing and out the discharge branch of the casing. When liquid is forced away from the center of the impeller, a vacuum is created and more liquid flows into the center of the impeller. Consequently there is a flow through the pump.
There are many forms of centrifugal pumps, including single-stage and multi-stage constructions. They may have impellers (vanes) with or without front shrouds, and may be single or double suction pumps. In any case, however, the abrasive nature of a solid/liquid mixture passing through a centrifugal slurry pump is such that the wetted components have to be made of wear-resistant material or wear-resistant liners have to be installed to reduce wear and prevent premature pump failure. The wear-resistant materials used to form the liners may be hard iron or elastomer, depending on the application and the size of the solids in the slurry. It has been found that the softer an elastomer liner is, the less wear is experienced. Lower softness (durometer), however, also means lower strength and greater flexibility of the material. This then requires some back support attached to the shell of the pump to resist the fluctuating pressure forces, and in some cases a vacuum.
Further problems with centrifugal pumps having liners installed therein are vacuum and cavitation. That is, as slurry is drawn into the eye of the impeller, a vacuum often results, and indeed, is expected, as it is the vacuum that draws the slurry into the pump. As would be expected, a vacuum has a collapsing effect, causing a soft liner to collapse inward. This seriously diminishes the capacity and operating characteristics of the pump. Additionally, where the pressure within the pump casing happens to be lower than the vapor pressure at the pump suction inlet, cavitation is inevitable. With a soft liner installed, flutter of the liner can occur, resulting in rapid degradation of the liner, and often the pump. This, then, requires that additional support be provides to the outer portions of the liners.
In a typical lined slurry pump, the pump casing is radially split and held together by bolts in order to enable the liners to be replaced. While it is easy to provide molded-in metal support plates to the faces of the elastomer liners and for these to be assembled by taking advantage of the split halves and the circularity, it is not so easy to provide support for the extended suction and discharge branch sections of the pump. It is possible, in the case of the discharge branch, to provide a relief in the face of the flange that a top hat section of the elastomer can be seated in. The split halves are easily assembled and sealed by providing an excess of elastomer (rubber) at the split and at the flange face. Special metal stiffeners can then be provided for any unsupported section of the branch. Providing support for the suction branch is not as simple since the suction is not split. Where the suction branch section has no support and the elastomeric liner is sufficiently soft, it is possible to provide the suction branch with a top hat flanged section that can be collapsed and pushed through the metal plate at the suction flange so that it is held in place at the discharge flange. Where, however, elastomers such as strengthened rubbers or urethanes are harder, it is more difficult, or in some cases impossible, to position the elastomer liner within the suction branch since the elastomer cannot be collapsed down for positioning. A further problem is that it has not been possible to provide proper support to the elastomer in a suction branch section because this would prevent collapsing the elastomer to fit it into the branch. The lack of support in such as case can cause fluttering, collapse and/or failure of the elastomer in the suction branch due to pulsing of the impeller vane and/or cavitation.
The present invention is directed to an abrasion-resistant liner assembly for the suction branch of a centrifugal pump that addresses the problems described above. Specifically, the assembly of the present invention may be easily installed on a single or multi-stage, single or multiple suction pump of the type having (1) at least one suction connection, or flange, for mating engagement with a suction source such as piping, (2) a suction inlet, (3) and, an annular region formed in the suction connection. While the present invention may be installed on a variety of pump types, exemplary installation on a single-stage, single suction centrifugal pump will be explained in detail herein
A preferred embodiment of the liner assembly includes a cylindrical liner having an outer, or inlet end, an inner end, and a diameter substantially conforming in dimension to the diameter of the suction branch inlet of the pump. A groove is formed in the outer surface of the liner and extends around the outer diameter of the liner to form a continuous recessed channel. A split-type seat ring with an inner diameter similar to that of the outer diameter of the recessed channel is positioned within the groove. The seat ring is dimensioned with an outer diameter larger than the outer diameter of the cylindrical liner, and hence, the suction branch, and substantially conforming in dimension to the diameter of the annular region formed in the suction flange of the pump. When seated in the groove, the seat ring engages the inner surface of the annular region, preventing the cylinder from moving axially inward toward the impeller of the pump. A seat ring holder of typically more rigid material is positioned adjacent the seat ring on the outer end of the liner. The seat ring holder has an inner diameter substantially conforming in dimension to the outer diameter of the liner and an outer diameter dimensioned to fit within the annular region. When the liner is positioned within the suction branch and the suction flange mated with a suction source (piping), the seat ring thus projects into the annular region and the seat ring holder prevents the liner from moving axially outward toward the connected suction source.
In another embodiment, the liner assembly includes a reinforcing cylinder attached to the outer surface of the elastomeric liner. The reinforcing cylinder may be formed of steel or other suitable rigid material and molded or adhered to the elastomeric liner. The cylinder provides additional support for operating conditions where the suction branch is subjected to vacuum and inlet cavitation.
While the abrasion-resistant liner assembly of the present invention is described with respect to installation in the suction branch of a pump, the same liner assembly may just as easily be installed in the discharge branch of a pump.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiments when considered in conjunction with the drawings. It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.